Oscillation producing means



y 29, 1941- w. ALBRICHT 2,251,025

0.5 CILLATION PRODUCING MEANS Filed Feb. 11, 1959 INV EN TOR.

' fit gm ALBR/CHT BY 7 v ATTORNEY.

Patented July 29, 1941 OSCILLATION PRODUCING BEAN S Wilhelm Albricht, Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application February 11, 1939, Serial No. 255,827 In the Netherlands March 22, 1938 4 Claims. (Cl. 250-36) This invention relates to a circuit arrangement for producing or amplifying ultra high frequency oscillations. To stabilize the frequency of an ultra short Wave generator it is desirable to connect an oscillatory circuit with divided selfinductance and capacity in the grid circuit of a discharge tube. Such oscillatory circuits .are also used in the grid circuit of back-coupled ultra short wave amplifiers.

I have found that these arrangements have a tendency to oscillate at a frequency which is not determined or at least not principally determined by the natural frequency of the oscillatory circuit with divided self-inductance and capacity connected in the grid circuit, but by the selfinduction and the capacity of the connecting leads of the oscillatory circuit to the grid and the cathode of the discharge tube and by any further available parasitic self-inductances and capacities,

According to the invention, the drawback is obviated by providing means known per se by which the back-coupling through internal impedances of the discharge tube or through impedances of the supply leads for the electrodes is removed and by providing an external feed back circuit which is connected to the grid circuit at a point of the oscillatory circuit with divided self-inductance and capacity connected in the grid circuit.

The invention is based on the recognition that the production of parasitic oscillations is avoided by providing the said well known neutralizing means, the external back-coupling being arranged in such a manner that the grid circuit presents a high impedance only for the desired oscillations, which impedance is substantially determined by the impedance of the oscillatory circuit with divided self-inductance and capacity whereas for voltages having a different frequency, which are carried back through the feed back circuit, said circuit is short-circuited through the oscillatory circuit.

The invention will be more clearly explained by reference to the accompanying drawing representing in Figs. 1 and 2, by way of example, two embodiments thereof.

Fig. 1 shows an arrangement for the production of ultra high frequency oscillations in which, according to the invention, back-coupling is avoided by making use of a screen grid tube I. The grid circuit of this tube comprises an oscillatory circuit 2 consisting of divided self-inductance and capacity, said circuit being connected through conductors 3 and 4 to the grid and cathode respectively of the tube l. The anode circuit comprises an oscillatory circuit 5 which is connected to a point of the oscillatory circuit 2 through an external feed back circuit including a feed back condenser 6.

To explain the operation of this arrangement, it is assumed that the screen grid 7' is not available in the discharge tube I. In this case the anode circuit is coupled to the grid circuit through the control-grid anode-capacity so that oscillations can be produced whose natural frequency is substantially determined by the grid cathode capacity and the self-induction and capacity of the conductors 3 and 4, since the oscillatory circuit 2 will generally constitute a short circuit for the frequency of these para-- sitic oscillations. If, however, use is made of a discharge tube comprising a screen grid 1, and an external feed back circuit is provided, the back-coupling substantially occurs solely through this circuit which is connected to the grid circuit at a point of the circuit 2. The oscillatory circuit constitutes a short circuit for all of the Voltages which are conveyed back through the feed back circuit and whose frequency i different from the natural frequency of the oscillatory circuit 2, thus avoiding the production of oscillations whose frequency is different from the desired frequency. Putting it another way, applicants invention relates to a tuned grid oscillator in which the presence of oscillations at desired and undesired parasitic frequencies depend, toan extent, on the feed-back within the vacuum tube. These undesired parasitic oscillations are caused by the inductance of the leads extending from the grid and cathode to the tuned grid circuit and by the internal feed-back of the oscillator produced by interelectrode capacity. This internal feed-back is eliminated in the present invention and external feed-back is used to a point on the tuned grid circuit where resonance occurs solely substantially at the desired frequency.

The arrangement shown in Fig. 2 comprises a discharge tube-I whose two grids are designed for the production of oscillations by means of an external back-coupling through a condenser E. The back-coupling across the capacity available between the two grid-s is removed by a neutralizing condenser B, which is connected on the one hand to the grid nearest the cathode and on the other hand to a point of the oscillatory circuit 5. The oscillations produced are utilized in an impedance 9 included in the anode circuit of the tube I To decouple the anode circuit and the generator part, thus counteracting the reaction of any load variations which may occur in the anode circuit, a screen grid may, if desired, be provided between the anode and the neighboring grid.

What is claimed is:

1. In an electron discharge device oscillator having a screen grid tube, a tuned circuit coupled between the anode and cathode, another tuned circuit and leads connecting said last tuned circuit to the control grid and cathode, and an external capacitive feed back path directly connected between a point on said anode tuned circuit and a point on said grid tuned circuit, whereby feed back potentials are applied to the control grid only through the impedance of the lead connecting said control grid to its associated tuned circuit, the leads from said cathode and grid to the tuned circuit associated therewith having such inductance as to cause the production of oscillations of undesired frequencies in the absence of the screen electrode in said tube.

2. ,An electron discharge device oscillator comprising a tube having cathode, control grid, and

anode electrodes; an anode oscillatory circuit between said anode and cathode, and a grid oscillatory circuit between said grid and cathode; leads from the control grid and cathode to two points in the oscillatory system, said leads having suificient length to develop parasitic oscillations; a screen grid in said device to prevent said parasitic oscillations; and a feed back for impressing potentials from the anode circuit upon said two points for producing the desired oscillations, whereby said feed back potentials are impressed upon said control grid and cathode only through said leads.

3. An electron discharge device oscillator having a cathode, a grid and another electrode for the production of oscillations, a grid circuit including a resonant system and leads connecting said resonant system to said cathode and grid, said leads including impedance which is of appreciable magnitude at a parasitic frequency,

said grid circuit as a whole having a natural frequency at a desired frequency and. at a parasitic frequency, an impedance network connected between said other electrode and said cathode and having therein currents of said parasitic frequency which tend to produce voltage fluctuations on said other electrode of such phase as to feed back energy in regenerative phase across said grid and cathode through the interelectrode anode-grid capacity of said device, means for reducing the interelec-trode capacity between said grid and other electrode to a Value too small to sustain oscillations at said parasitic frequency, and a capacitive connection from said impedance network to a point on said resonant system whose impedance is high solely at the desired frequency.

4. An oscillation generating circuit comprising in combination, a vacuum tube including a hot cathode and input and output cold electrodes cooperating therewith, a circuit connecting said hot cathode and one of said cold electrodes, a circuit connecting said hot cathode and the other of said cold electrodes, one of said circuits exhibiting resonance at substantially a desired frequency, the connections of said one circuit to said tube electrodes being such as to create therebetween an additional resonance at a parasitic frequency substantially different from said desired frequency, whereby direct capacity between said cold electrodes tends to produce parasitic oscillations, means for substantially eliminating the effect of direct capacity between said cold electrodes whereby all coupling between said circuits by way of direct capacity between said cold electrodes is substantially eliminated, and a capacity connected between a point in said other circuit and a point in said one circuit such that between the last named point and said cathode substantial resonance occurs solely at substantially said desired frequency, whereby oscillations of said desired frequency are produced and parasitic oscillations are prevented.

VVILHELM ALBRICHT. 

